Role of melatonin in the pathophysiology of migraine: implications for treatment

Serum melatonin levels and in a sample of Iranian patients with migraine

Migraine, a complex disorder, is characterized by recurrent headache episodes. The production of melatonin in the pineal gland, which is crucial for controlling circadian rhythms and sleep-wake cycles, is altered in various conditions, including neurological disorders such as migraine. Recent studies underscore the significance of serum melatonin levels in patients with chronic and episodic migraine, the focus of this study. This case‒control study, conducted from September 2017 to June 2020 in Tehran, Iran, selected potential participants aged 18-65 years from a headache clinic at Sina Hospital (affiliated with Tehran University of Medical Sciences). Both episodic migraine and chronic migraine were diagnosed following the diagnostic criteria in the International Classification of Headache Disorders' third edition. Melatonin levels were measured according to the instructions of the ELISA kits. There were significant differences in the frequency of headache days and the duration of abortive medication usage between the two groups (P value < 0.001). Besides, analysis revealed significantly lower serum melatonin levels in patients with episodic ((80.45-45.06) 72.83) and chronic migraine ((154.34-63.34) 70.38, P value < 0.001) than in healthy controls (281.25-160.86) 280). Although no considerable differences were found between episodic and chronic migraine patients, the current study demonstrated that serum melatonin levels were substantially greater in healthy controls than in patients with migraine.

Consensus of the Brazilian Headache Society (SBCe) for prophylactic treatment of episodic migraine: part II

BACKGROUND

Migraine affects 1 billion people worldwide and > 30 million Brazilians; besides, it is an underdiagnosed and undertreated disorder.

OBJECTIVE

The need to disseminate knowledge about the prophylactic treatment of migraine is known, so the Brazilian Headache Society (SBCe, in the Portuguese acronym) appointed a committee of authors with the objective of establishing a consensus with recommendations on the prophylactic treatment of episodic migraine based on articles from the world literature as well as from personal experience.

METHODS

Meetings were held entirely online, with the participation of 12 groups that reviewed and wrote about the pharmacological categories of drugs and, at the end, met to read and finish the document. The drug classes studied in part II of this Consensus were: antihypertensives, selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, calcium channel blockers, other drugs, and rational polytherapy.

RESULTS

From this list of drugs, only candesartan has been established as effective in controlling episodic migraine. Flunarizine, venlafaxine, duloxetine, and pizotifen were defined as likely to be effective, while lisinopril, enalapril, escitalopram, fluvoxamine, quetiapine, atorvastatin, simvastatin, cyproheptadine, and melatonin were possibly effective in prophylaxis of the disease.

CONCLUSIONS

Despite an effort by the scientific community to find really effective drugs in the treatment of migraine, given the large number of drugs tested for this purpose, we still have few therapeutic options.

Melatonin as a treatment for migraine sufferers: a systematic review

Background

Migraine is a primary headache with a prevalence of 12–20% in the world. Approximately 38% sufferers were indicated for prophylactic therapy, but only a small proportion (3–13%) received prophylactic therapy. The role of melatonin in migraine is to protect the brain against toxins through anti-free radical activity, inhibition of the release of inflammatory factors and neurotransmitters.

Results

This review uses the PRISMA protocol and uses source from Pubmed. A total of 142 articles were found according to the search strategy. 5 articles were collected with a randomized-controlled trial design that matched the inclusion criteria. Of the 5 articles, there were only 2 articles that proved significant where melatonin gave better results compared to placebo in migraine sufferers, especially in the frequency of attacks, duration, and reduction in the use of other analgesics. Based on the dose and duration of melatonin administration, although most use a dose of 3 mg melatonin with a duration of 2–3 months, this still needs to be investigated further because the available data are not sufficient. In addition, the use of melatonin before going to bed at night is said to be better because it is associated with the majority of side effects that occur, namely sleepiness.

Conclusion

Studies on melatonin and migraine with a randomized-controlled trial design are still limited so there is not enough evidence to support the administration of melatonin as a treatment for migraine sufferers, including the safety and side effects, especially for a long period of time.

The Pathogenetic Role of Melatonin in Migraine and Its Theoretic Implications for Pharmacotherapy: A Brief Overview of the Research

Migraine is a chronic disease of global concern, regardless of socio-economic and cultural background. It most often and intensely affects young adults, especially women. Numerous mechanisms of a migraine attack have been identified (disturbances in the reaction of vessels, functions of neurotransmitters, cortical neurons, ion channels, receptors, the process of neurogenic inflammation), and many of its symptoms can be explained by activation of the hypothalamus and disturbances in its communication with other brain regions (including the brainstem). Numerous neuropeptides and neurochemical systems also play a role in migraine. One of them is melatonin, a hormone that allows the body to adapt to cyclically changing environmental and food conditions. In this article, we present the pathophysiological basis of melatonin release from the pineal gland and other tissues (including the intestines) under the influence of various stimuli (including light and food), and its role in stimulating the brain structures responsible for triggering a migraine attack. We analyze publications concerning research on the role of melatonin in various headaches, in various stages of migraine, and in various phases of the menstrual cycle in women with migraine, and its impact on the occurrence and severity of migraine attacks. Melatonin as an internally secreted substance, but also present naturally in many foods. It is possible to supplement melatonin in the form of pharmaceutical preparations, and it seems, to be a good complementary therapy (due to the lack of significant side effects and pharmacological interactions) in the treatment of migraine, especially: in women of childbearing age, in people taking multiple medications for other diseases, as well as those sensitive to pharmacotherapy.

From basic mechanisms to therapeutic perspectives in cluster headache

PURPOSE OF REVIEW

The pathophysiological understanding of cluster headache has evolved significantly over the past years. Although it is now well known that the trigeminovascular system, the parasympathetic system and the hypothalamus play important roles in its pathomechanism, we increasingly understand the functional role several neurotransmitters and hormones play in the communication between these structures.

RECENT FINDINGS

This work will give an overview of the current understanding of the role of calcitonin gene-related peptide, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, melatonin and orexins in cluster headache. On the basis of recent evidence, this study will also review the relevance of the monoclonal calcitonin gene-related peptide antibody galcanezumab as well as the sleep-regulating hormone melatonin in the treatment of cluster headache.

SUMMARY

Herein, we aim to review the basic mechanisms implicated in the pathophysiology of cluster headache and how the increased mechanistic understanding may lead to the discovery of novel therapeutic targets.

Investigating the Frequency of Infantile Colic in Children with Migraine

Infantile colic is a common problem observed within the first 3 months of life in infants and is a common cause of crying among infants. Migraine is a common cause of recurrent primary headaches during childhood. The pathogenesis of migraine and colic has remained unknown, but various factors seem to be involved. Patients with migraine may have a medical history of infantile colic, and infantile colic is considered an early manifestation of migraine. In this study, we investigate the frequency of history of infantile colic in 6- to 14-year-old children with migraines. In this case–control study, 80 children with the diagnosis of migraine and 100 children without migraine, all within the age range of 6 to 14 years, were included. A checklist was completed for each person about the background information and history of infantile colic as well as the history of migraine in parents. Among the children with migraine, 92.5%, and in the control group, 10%, had a familial history of migraine. Also, among the children with migraine, 61.25%, and in the control group, 4%, had a history of infantile colic. The obtained results showed that the frequency of a history of infantile colic was significantly higher in the case group than in the control group. This study provides some evidence regarding the presence of association between infantile colic as well as the familial history of migraines and developing migraines in the future. However, due to some limitations of the retrospective manner of the study, the results should be completed with future studies.

Targets for migraine treatment: beyond calcitonin gene-related peptide

PURPOSE OF REVIEW

Despite the development of several medications for the acute and preventive treatment of migraine, there are still many patients in whom lack of efficacy, tolerability, interactions or contraindications make other options necessary. CGRP-based drugs have opened the door to a new era of migraine-targeted treatments. Beyond CGRP, there are other promising targets covered here.

RECENT FINDINGS

For the acute treatment of migraine, 5-HT1F receptor agonists, ditans, are now available. Unlike triptans, 5-HT1B/1D receptor agonists, cardiovascular disease is not a contraindication for the use of ditans. The first study on a monoclonal antibody targeting PAC1 receptor was negative, although this may not be the end for the pituitary adenylate cyclase-activating polypeptide (PACAP) pathway as a target.

SUMMARY

Following positive phase-III clinical trials, lasmiditan is the first ditan to be FDA-approved. PACAP has experimental evidence suggesting a role in migraine pathophysiology. As for CGRP, the presence of PACAP in key migraine structures along with positive provocative tests for both PACAP-38 and PACAP-27 indicate this pathway may still be a pharmacological target. Glutamate-based targets have long been considered in migraine. Two clinical trials with memantine, an NMDA-R antagonist, for the preventive treatment of migraine have now been published. The hypothalamus has also been implicated in migraine pathophysiology: the potential role of orexins in migraine is discussed. Acid-sensing ion channels, as well as amylin-blocking drugs, may also become migraine treatments in the future: more research is warranted.

Financial Stress Interacts With CLOCK Gene to Affect Migraine

Previous studies suggested that both maladaptive stress response and circadian dysregulation might have a role in the background of migraine. However, effects of circadian genes on migraine have not been tested yet. In the present study, we investigated the main effect of rs10462028 of the circadian locomotor output cycles kaput (CLOCK) gene and its interaction with different stress factors on migraine. In our cross-sectional study 2,157 subjects recruited from Manchester and Budapest completed the ID-Migraine questionnaire to detect migraine type headaches (migraineID). Additional stress factors were assessed by a shortened version of the Childhood Trauma Questionnaire, the List of Threatening Experiences questionnaire, and a validated questionnaire to identify financial difficulties. Rs10462028 showed no main genetic effect on migraineID. However, chronic stress indexed by financial difficulties showed a significant interaction effect with rs10462028 (p = 0.006 in recessive model) on migraineID. This result remained significant after correction for lifetime bipolar and unipolar depression and was replicated in both subsamples, although only a trend effect was reached after Bonferroni-correction, which is the strictest correction not considering interdependences. Childhood adversity (CHA) and Recent negative life events (RLE) showed no significant gene × stress interaction with rs10462028. In addition, in silico analysis demonstrated that the genetic region tagged by rs10462028 alters the binding of several miRNAs. Our exploratory study suggests that variations in the CLOCK gene, with moderating effect on gene function through miRNA binding, in interaction with financial difficulties might influence the risk of migraine-type headaches. Thus, financial hardship as a chronic stress factor may affect migraine through altering circadian rhythms.

Circadian Variation of Migraine Attack Onset: A Review of Clinical Studies

Several studies suggested that migraine attack onset shows a circadian variation; however, there has not been an overview and synthesis of these findings. A PubMed search with keywords "migraine" AND "circadian" resulted in ten studies directly investigating this topic. Results of these studies mostly show that migraine attacks follow a monophasic 24-hour cyclic pattern with an early morning or late night peak while other studies reported an afternoon peak and also a biphasic 24-hour cycle of attacks. The identified studies showed methodological variation including sample size, inclusion of medication use, comorbidities, and night or shift workers which could have contributed to the contradictory results. Several theories emerged explaining the diurnal distribution of migraine attacks suggesting roles for different phenomena including a morning rise in cortisol levels, a possible hypothalamic dysfunction, a circadian variation of migraine triggers, sleep stages, and a potentially different setting of the circadian pacemaker among migraineurs. At the moment, most studies show an early morning or late night peak of migraine attack onset, but a significant amount of studies reveals contradictory results. Further studies should investigate the arising hypotheses to improve our understanding of the complex mechanism behind the circadian variation of migraine attacks that can shed light on new targets for migraine therapy.

Therapeutic role of melatonin in migraine prophylaxis: A systematic review

BACKGROUND

Melatonin is the "clock factor" generated from pineal gland dominating regular circadian rhythm in humans. Migraine is one of the most severe and debilitating primary headache disorders. Thus far, many diseases have been found to associate with melatonin, including the migraine. Therefore, melatonin's therapeutic potential for migraine is drawing attention.

OBJECTIVES

The aim of this study is to offer a systematic review of extant data of melatonin in migraine prophylaxis and to provide clinical implications and specific recommendations for future studies.

DATA SOURCES AND STUDY METHODS

A systematic research was conducted in September 2018 by using PubMed and Google Scholar databases to search for science literature published after 1988.

RESULTS

In all, 7 eligible articles were identified, including 4 randomized controlled studies and 3 observational studies. Due to high heterogeneities and limited number of studies, meta-analysis was not feasible, and only systematic review was performed. The results show that present evidence cannot claim melatonin's effectiveness according to the conflicting outcomes; however, the two negative outcomes of melatonin not different from placebo and melatonin inferior to amitriptyline are possible under-powering because of methodological, pharmacological, and therapeutic shortcomings. Observational studies also support melatonin's efficacy in migraine. As a result, melatonin is very likely to benefit migraine in prophylaxis and may have a similar effectiveness to other main preventive medications. Immediate-release melatonin 3 mg was established as effective, melatonin receptor agonist (Agomelatine) 25 mg and prolonged-release melatonin 4 mg were observed efficacious in observational studies. Melatonin displayed ineffective in the 2-month trial; thus, 3 months or more may be an enough duration for migraine therapy. Despite melatonin being generally safe, emerging literature is illustrating that a few severe adverse effects can be caused by melatonin, for example, liver injuries, reproductive system dysfunctions, and detrimental immunostimulation.

CONCLUSIONS

Melatonin is very likely to be a promising alternative for migraine prophylaxis. Current literature examining melatonin's efficacy in migraine prevention is growing, but still limited. Future studies of perfect design in methodology, pharmacology, and therapeutics are needed to achieve a deeper awareness of melatonin's role in migraine as well as more studies to explore the safety issues of melatonin medicine.

The effect of melatonin on gene expression of calcitonin gene-related peptide and some proinflammatory mediators in patients with pure menstrual migraine

The neuropeptide calcitonin gene-related peptide (CGRP), a potent vasoactive and a marker of trigeminal inflammation, has been considered as an important mediator in various types of migraine such as pure menstrual migraine. Earlier studies have shown that CGRP can modulate the synthesis and release of other inflammatory factor including nitric oxide (NO) and interleukin-1beta (IL-1β) from trigeminal ganglion glial cells. Exogenous melatonin protects the tissues from inflammatory damages. The goal of this study was to determine the anti-inflammatory effects of melatonin on the CGRP expression, inducible nitric oxide synthase (iNOS) activity, NO, and IL-1β release in cultured peripheral blood mononuclear cells (PBMCs) from pure menstrual migraine patients and healthy subjects. This study was performed on 12 pure menstrual migraine patients and 12 age-and sex-matched healthy subjects. PBMCs were isolated and treated with melatonin for 12 h at pharmacological dose. Gene expression was evaluated by real-time PCR. CGRP and IL-1β proteins in culture supernatant were determined by ELISA method. iNOS activity in PBMCs was determined by colorimetric assays. Total nitrite as an indicator of NO concentrations in the culture supernatants was measured using Griess method. We found that melatonin treatment significantly decreases mRNA expression of CGRP release, NO production, and iNOS activity in the patient groups. Taken together, it appears that melatonin reduces inflammation through decreasing CGRP level and iNOS activity in the patients with migraine; however, further studies are needed in this regard.

Shorter sleep duration is associated with social impairment and comorbidities in ASD

Sleep disturbance, particularly insomnia, is common in children with autism spectrum disorders (ASD). Furthermore, disturbed sleep affects core symptoms and other related comorbidities. Understanding the causes and consequences of sleep disturbances in children with ASD is an important step toward mitigating these symptoms. To better understand the connection between sleep duration and ASD severity, we analyzed ASD-related symptoms using the Autism Diagnostic Interview-Revised (ADI-R), Autism Diagnostic Observation Schedule (ADOS), IQ scores, and parent reports of the average amount of time slept per night that were available in the medical histories of 2,714 children with ASD in the Simons Simplex Collection (SSC). The mean (SD) sleep duration was 555 minutes. Sleep duration and severity of core ASD symptoms were negatively correlated, and sleep duration and IQ scores were positively correlated. Regression results indicated that more severe social impairment, primarily a failure to develop peer relationships, is the core symptom most strongly associated with short sleep duration. Furthermore, increased severity for numerous maladaptive behaviors assessed on the Child Behavior Checklist, as well as reports of attention deficit disorder, depressive disorder, and obsessive compulsive disorder were associated with short sleep duration. Severity scores for social/communication impairment and restricted and repetitive behaviors (RRB) were increased, and IQ scores were decreased, for children reported to sleep ≤420 minutes per night (lower 5th percentile) compared to children sleeping ≥660 minutes (upper 95th percentile). Our results indicate that reduced amounts of sleep are related to more severe symptoms in children with ASD. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1221-1238. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Sleep quality, morningness-eveningness preference, mood profile, and levels of serum melatonin in migraine patients: a case-control study

The melatonin as the pineal gland's secretory product is implicated in the pathophysiology of migraine. Melatonin has critical functions in human physiology, and research underscores the importance of melatonin in circadian rhythm, sleep, and mood regulation. Clinical observations have indicated that migraine attacks have a seasonal, menstrual, and circadian timing, suggesting that chronobiological mechanisms and their alterations may causally involve in the etiology of the disease. However, the topic has received relatively little attention in the migraine literature. Associations between melatonin, circadian preference, sleep, and mood states were investigated in the current study. Fifty-five patients (47 females and 8 males) were compared to 57 gender and age-matched control subjects (40 females and 17 males). A socio-demographical questionnaire, the Beck Depression Inventory, Beck Anxiety Inventory (BAI), Pittsburgh Sleep Quality Index (PSQI), Profile of Mood States (POMS), and Morningness-Eveningness Questionnaire were administered to volunteers. Blood samples were taken from all participants at about 1:00 AM in an unlit room not to hamper melatonin secretion, and blood melatonin levels were measured using quantitative ELISA test. In comparison with controls, melatonin levels were significantly lower among migraine patients. Migraineurs reported significantly greater scores on the BAI, confusion-bewilderment subscale of the POMS, and total and sleep latency subscale of the PSQI. Migraine patients who had nausea during the migraine attacks and who reported bouts relevant to certain food consumption, such as cheese or chocolate, had significantly lower levels of melatonin. Contrarily, groups did not reveal statistically substantial difference in circadian preferences.

Pain perception in healthy young men is modified by time-of-day and is modality dependent

OBJECTIVE

Several physiological processes exhibit 24-hour oscillations termed circadian rhythms. Despite numerous investigations on the circadian dynamics of pain perception, findings related to this issue remain inconsistent. This study aimed to assess the effect of time-of-day on multimodal experimental pain perception in healthy males, including "static" and "dynamic" quantitative sensory tests.

DESIGN

A random order tests were performed in the morning, afternoon and evening.

SUBJECTS

Forty-eight healthy males (25.9 ± 4.7 years old).

METHODS

Three different pain modalities i) mechanical (pain threshold, tolerance, and intensity), ii) heat (pain threshold and intensity), iii) cold (pain threshold measured in °C and in seconds and cold pain tolerance and intensity) utilizing nine "static" pain parameters, and two "dynamic" pain paradigms i) temporal summation and ii) conditioned pain modulation were assessed in each session.

RESULTS

Pain scores varied significantly in six pain parameters during the day. Specifically, lower pain scores were found in the morning for cold pain threshold (in seconds and in °C), cold pain intensity, cold pain tolerance, heat pain threshold and intensity. There were no significant diurnal differences in the mechanical evoked pain parameters or in either of the "dynamic" pain paradigms.

CONCLUSIONS

Thermal pain scores varies during the day and morning seems to be the time-of-day most insensitive to pain. Also, dynamic tests and the mechanical pain model are not appropriate for detecting diurnal variability in pain. The results of this study may be partially explained by a potential analgesic effect of some hormones known to have diurnal variation (e.g., melatonin and cortisol).

Circadian melatonin rhythm and excessive daytime sleepiness in Parkinson disease

IMPORTANCE

Diurnal fluctuations of motor and nonmotor symptoms and a high prevalence of sleep-wake disturbances in Parkinson disease (PD) suggest a role of the circadian system in the modulation of these symptoms. However, surprisingly little is known regarding circadian function in PD and whether circadian dysfunction is involved in the development of sleep-wake disturbances in PD.

OBJECTIVE

To determine the relationship between the timing and amplitude of the 24-hour melatonin rhythm, a marker of endogenous circadian rhythmicity, with self-reported sleep quality, the severity of daytime sleepiness, and disease metrics.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional study from January 1, 2009, through December 31, 2012, of 20 patients with PD receiving stable dopaminergic therapy and 15 age-matched control participants. Both groups underwent blood sampling for the measurement of serum melatonin levels at 30-minute intervals for 24 hours under modified constant routine conditions at the Parkinson's Disease and Movement Disorders Center of Northwestern University.

INTERVENTIONS

Twenty-four hour monitoring of serum melatonin secretion.

MAIN OUTCOMES AND MEASURES

Clinical and demographic data, self-reported measures of sleep quality (Pittsburgh Sleep Quality Index) and daytime sleepiness (Epworth Sleepiness Scale), and circadian markers of the melatonin rhythm, including the amplitude, area under the curve (AUC), and phase of the 24-hour rhythm.

RESULTS

Patients with PD had blunted circadian rhythms of melatonin secretion compared with controls; the amplitude of the melatonin rhythm and the 24-hour AUC for circulating melatonin levels were significantly lower in PD patients (P < .001). Markers of the circadian phase were not significantly different between the 2 groups. Compared with PD patients without excessive daytime sleepiness, patients with excessive daytime sleepiness (Epworth Sleepiness Scale score ≥10) had a significantly lower amplitude of the melatonin rhythm and 24-hour melatonin AUC (P = .001). Disease duration, Unified Parkinson's Disease Rating Scale scores, levodopa equivalent dose, and global Pittsburgh Sleep Quality Index score in the PD group were not significantly related to measures of the melatonin circadian rhythm.

CONCLUSIONS AND RELEVANCE

Circadian dysfunction may underlie excessive sleepiness in PD. The nature of this association needs to be explored further in longitudinal studies. Approaches aimed to strengthen circadian function, such as timed exposure to bright light and exercise, might serve as complementary therapies for the nonmotor manifestations of PD.

Effect of sex and estrogens on neuronal activation in an animal model of migraine

OBJECTIVE

In this study, we evaluated the influence of sex and estrogen treatment on nitroglycerin (NTG)-induced neuronal activation in the rat brain.

BACKGROUND

Systemic NTG activates cerebral nuclei of rat involved in nociceptive transmission, as well as in neuroendocrine and autonomic functions. These changes are considered relevant for migraine, since NTG consistently induces spontaneous-like attacks in migraineurs.

METHODS

Intact and castrated male and female rats, and castrated female rats treated with estradiol benzoate (or placebo) were injected with NTG and sacrificed after 4 hours. Rats were perfused, and their brains were processed for Fos protein, a marker of neuronal activation.

RESULTS

Data showed a reduced expression of NTG-induced Fos protein in the paraventricular nucleus (PVH), supraoptic nucleus (SON), and nucleus trigeminalis caudalis (SPVC) of male rats in comparison with female rats. Furthermore, in castrated female rats, NTG-induced neuronal activation was reduced in PVH, SON, central nucleus of the amygdala (AMI), nucleus tractus solitarius (NTS), area postrema (AP), and SPVC, while in castrated male rats Fos expression was reduced uniquely in the SPVC. Chronic administration of estrogens restored Fos protein expression in PVH, SON, AMI, NTS, AP, and SPVC in castrated female rats.

CONCLUSION

These data provide a support for the existence of a sexual dimorphism in NTG-induced neuronal activation, and they prompt a specific model for evaluating and modulating the influence of estrogens upon the cerebral structures implicated in the pathophysiology of migraine.

Immunohistochemical and biomolecular identification of melatonin 1a and 1b receptors in rat vestibular nuclei

OBJECTIVE

The aim of this study was to examine the localizations and expressions of melatonin 1a (MT1a) and 1b (MT1b) receptors in rat vestibular nuclei by immunohistochemical staining and reverse transcriptase-polymerase chain reaction.

MATERIALS AND METHODS

Twenty male Sprague-Dawley rats were used in this study. Antibodies for the MT1a and MT1b receptors were used in 10 rats, respectively. A further 10 animals were sacrificed for RT-PCR. Tissues containing medial vestibular nuclei were selectively isolated from brain stem slices for RT-PCR.

RESULTS

MT1a and MT1b receptor immunopositive neurons were found to be distributed throughout the four major vestibular nuclei. Both receptors were primarily detected in neuronal somata and their proximal dendrites. The presences of the mRNAs of the MT1a and MT1b receptors were confirmed by RT-PCR in medial vestibular nuclei and trigeminal ganglia.

CONCLUSIONS

The present study demonstrates, for the first time, that MT1a and MT1b receptors are localized and expressed in rat vestibular nuclei. This study provides additional insight into the role of melatonin receptors during vestibular signal processing.

Sleep and headache: the biological basis

Sleep and trigeminal pain processing share several common pathways with respect to neurotransmission and functions of distinct brain areas. In this review, the role of the most important brain stem and midbrain regions for this link is discussed. The central structure involved in both headache and sleep is the hypothalamus in which the orexinergic neurons originate. These neurons project to the periaqueductal grey and are probably the anatomic and physiological link between headache and sleep. Another relevant system for this interrelationship is the melatonin metabolism. However, basic research in this field is still very preliminary and a holistic hypothesis on how sleep physiology impacts headache and vice versa is still missing.

Some questions provoked by a chronic headache (with mixed migraine and cluster headache features) in a woman with a pineal cyst. Answers from a literature review

The main known function of the pineal gland in humans is the production of melatonin. Benign cysts of the gland have been related to headache, although the mechanism of production of this assumed clinical manifestation has not been clearly determined, due to the lack of large prospective studies. The question is complicated by the fact that pineal cysts are frequently found on brain magnetic resonance imaging. Much has been published about the possible role of benign pineal cysts in the pathophisiology of headaches and the potential of melatonin in headache therapy, as well as in other disorders. The aim of this article is to review the current state of the suject. We have tried to place accurately the relation between headache and pineal cysts based on the available evidence, as well as the actual role of melatonin in physiology and pharmacology, more specifically in headache therapy. We include a clinical case to illustrate the subject.

Antinociceptive effects of melatonin in a rat model of post-inflammatory visceral hyperalgesia: a centrally mediated process

Previous reports suggest that melatonin may play an important role in visceral nociception and neurogenic inflammation. We aimed to examine the role of melatonin on visceral hypersensitivity and to explore the site of action using a rat model of post-inflammatory visceral hyperalgesia. In all rats, a baseline viscero-motor response (VMR) to graded colorectal distension (CRD; 10-60mmHg) was recorded prior and 1 week following tri-nitrobenzenesulfonic acid (TNBS) induced colonic inflammation. Melatonin (30, 45 or 60mg/kg, ip) was given 20min before testing the VMR in naïve and TNBS-treated rats. Extracellular single-unit recordings were made from CRD-sensitive pelvic nerve afferent (PNA) fibers and lumbosacral (LS) spinal neurons in TNBS-treated animals. The effect of melatonin (60mg/kg) was examined on responses of PNAs and spinal neurons to graded CRD. In separate experiments, luzindole (non-specific MT(1)/MT(2) receptor antagonist) or naltrexone (non-specific opiod receptor antagonist) was injected prior to melatonin. Following TNBS, there was a significant increase in the VMR to CRD compared to baseline. This increase was attenuated by melatonin (60mg/kg) at pressures >20mmHg. The same dose of melatonin had no effect on the VMR in naïve animals. In TNBS-treated rats, melatonin significantly attenuated the responses of CRD-sensitive spinal neurons to CRD, but had no effect in spinal transected rats or PNA fibers. Both luzindole and naltrexone blocked melatonin's effect on the VMR and LS spinal neurons. Results indicate melatonin's antinociceptive effects are not via a peripheral site of action but rather a supra-spinal process linked to the central opioidergic system.

Sleep and headache

There is a strong interaction between sleep and headache. Sleep and headache disorders overlap epidemiologically, and share elements of anatomy and physiology. Perhaps as a result, their treatment is often mutually interdependent. Despite this, headache and sleep disorders tend to be treated separately, by different subspecialties of neurology. The headache disorders and their relationship to sleep, the commonalities of headache and sleep pathophysiology, and headache disorders that are particularly susceptible to sleep modulation (and vice versa) are reviewed. Practical management advice for sleep-modulated headaches is provided.

Melatonin: a hormone that modulates pain

AIMS

Melatonin is a hormone synthesized principally in the pineal gland that has been classically associated with endocrine actions. However, several lines of evidence suggest that melatonin plays a role in pain modulation. This paper reviews the available evidence on melatonin's analgesic effects in animals and human beings.

MAIN METHODS

A medline search was performed using the terms "melatonin", "inflammatory pain", "neuropathic pain", "functional pain", "rats", "mice", "human", "receptors", "opioid" and "free radicals" in combinations.

KEY FINDINGS

The antinociceptive effect of melatonin has been evaluated in diverse pain models, and several findings show that melatonin receptors modulate pain mechanisms as activation induces an antinociceptive effect at spinal and supraspinal levels under conditions of acute and inflammatory pain. More recently, melatonin induced-antinociception has been extended to neuropathic pain states. This effect agrees with the localization of melatonin receptors in thalamus, hypothalamus, dorsal horn of the spinal cord, spinal trigeminal tract, and trigeminal nucleus. The effects of melatonin result from activation of MT(1) and MT(2) melatonin receptors, which leads to reduced cyclic AMP formation and reduced nociception. In addition, melatonin is able to activate opioid receptors indirectly, to open several K(+) channels and to inhibit expression of 5-lipoxygenase and cyclooxygenase 2. This hormone also inhibits the production of pro-inflammatory cytokines, modulates GABA(A) receptor function and acts as a free radical scavenger.

SIGNIFICANCE

Melatonin receptors constitute attractive targets for developing analgesic drugs, and their activation may prove to be a useful strategy to generate analgesics with a novel mechanism of action.

Understanding the causes and prevention of menstrual migraine: the role of estrogen

Menstruation increases the risk of migraine in susceptible women. In a subpopulation of women with menstrual migraine, headaches occurring in association with onset of menses may be more severe and of longer duration than headaches experienced by the same woman at other times of her menstrual cycle. Although menstrual migraines share many clinical characteristics of other types of migraines, their occurrence is predictable provided that the patient has regular menstrual cycles. Therefore, short-term prevention regimens can be considered for women whose headaches are not adequately managed with acute therapies.

Deorphanisation of G protein-coupled receptors: A tool to provide new insights in nervous system pathophysiology and new targets for psycho-active drugs

G protein-coupled receptors represent the largest family of membrane receptors translating extracellular into intracellular signals. Endogenous ligands for these receptors range from physical stimuli (e.g., light and odorants) to ions and chemical transmitters, such as "classical" biogenic amines, nucleotides and peptides. Some of these receptors are pathologically altered in neurodegenerative and psychiatric diseases and indeed represent the target for a variety of already marketed psycho-active drugs. With the publication of the human genome, it has become evident that there still are many "orphan" G protein-coupled receptors, i.e., receptors responding to yet-unidentified endogenous ligands. A large amount of these receptors are expressed in nervous tissues, but, apart from their molecular structure, we have no information concerning their physiological roles and alterations in disease states. In this review, we summarise the advancements and pitfalls of the strategies that have been exploited in recent years to "deorphanise" some of these receptors. We also show how, in some cases, this deorphanisation process has resulted in the identification of new potential targets for drug development as well as in the discovery of previously unknown neurotransmitters, including bioactive peptides and substances that had been merely known as metabolic intermediates. We envisage that the deorphanisation of the remaining orphan G protein-coupled receptors will further advance our knowledge of nervous system pathophysiology and unveil additional targets for new therapeutic approaches to human diseases, including psychosis, depression, anxiety, pain and aging-associated neurodegenerative disorders.